Effect of dietary modificatio of muscle long-chainN-3 fatty acid on plasma insulin and lipid metabolite, carcass traits, and fat deposition in lambs

In a previous study we showed that feeding fish meal significantly increased muscle long chain n-3 fatty acids (FA) and hot carcass weight. In this study we compared the effect of fish meal and fish oil on increasing muscle long-chain FA. We also investigated whether the increase in carcass weight was due to the effect of dietary enrichment of muscle long-chain n-3 FA on muscle membrane phospholipids and(or) to rumen by-pass protein provided by fish meal. Forty crossbred ([Merino x Border Leicester] x Poll Dorset) wether lambs between 26 and 33 kg BW were randomly assigned to one of five treatments: 1) basal diet of oaten:lucerne chaff (Basal); 2) Basal + fish meal (9% DM) = FM; 3) Basal + fish oil (1.5% DM) with protected sunflower meal (9% DM ) = FOSMP; 4) Basal + fish oil (1.5% DM) = FO; or 5) Basal + protected sunflower meal (10.5% DM) = SMP. Daily intake of ME (9.60 - 10.5 MJ ME/d) and CP (150 to 168 g/d) in all treatments was kept similar by varying the ratio of oaten:lucerne chaff and by feeding the animals at 90% ad libitum intake. Blood samples were collected at the start of the experiment and on the day (d 42) prior to slaughter. Lambs were then slaughtered at a commercial abattoir. At 24 h postmortem carcass traits were measured and longis-simus thoracis muscle taken for analysis of FA of phospholipid and triglyceride fractions. Lambs fed FO and FOSMP showed a marked increase in muscle longchain n-3 FA (P < 0.001) and a reduction in magnitude of the rise in insulin concentration (P < 0.001) after feeding compared with lambs fed Basal and SMP diets. Lambs in FM had a moderate increase (P < 0.001) in muscle long-chain n-3 FA content. Compared with Basal diet, both plasma total cholesterol (P < 0.02) and high-density lipoprotein cholesterol (P < 0.001) levels were greater in SMP and less in FO and FOSMP treat- ments. The i.m. fat content was reduced (P < 0.05) in FM and FO treatments, but carcass weight was increased only with fish meal (P < 0.03). Adding SMP to FO produced muscle with an intermediate level of i.m. fat, whereas muscle long-chain n-3 FA, i.m. fat, and insulin concentration were unchanged with SMP treatment. These results indicate that an increase in carcass weight in FM may be due to the supply of ruminally undegraded protein. They also suggest that fish oil along with fish meal can increase long-chain n-3 FA content in phospholipid of muscle membrane. This may be associated with reduced i.m. fat content and altered insulin action and lipoprotein metabolism.

Dietary manipulation of muscle long-chain omega-3 and omega-6 fatty acids and sensory properties of lamb meat

The effects of dietary manipulation of muscle long-chain omega-3 fatty acids (FA) on sensory properties of cooked meat in second cross ([Merino×Border Leicester]×Poll Dorset) wether lambs were evaluated. Lambs fed dietary supplements of fish meal (FM, Exp. 1) and fish oil (FO, Exp. 2) showed moderately (P<0.01) and markedly (P<0.001) increased muscle long-chain omega-3 FA content compared with those fed the basal diet of lucerne chaff and oat chaff. Protected canola seed (PCS, Exp. 1) significantly (P<0.001) increased omega-6 FA content of the longissimus muscle. In each of the 2 experiments (1 and 2), after being fed experimental diets for 6 weeks lambs were slaughtered at a commercial abattoir. At 24 h post-mortem (PM) the semitendinosus and biceps femoris muscles were removed from animals and stored at −20°C until evaluation of sensory properties using experienced panel members. The muscle samples were stored for 3 (Exp. 1) and 12 (Exp. 2) months then removed, thawed and cooked for sensory evaluation. The meat samples were cooked under standardized conditions in a convection microwave at 180°C (20–25 min) to an internal temperature of 75°C. Cooked samples were tested for flavour, aroma, juiciness and overall palatability. The significant increase in muscle long-chain omega-3 with FM (Exp. 1 and 2) and FO (Exp. 2) or omega-6 FA with PCS (Exp. 1) were not detrimental to sensory panel evaluations of flavour or aroma of cooked meat when compared with the basal diet. However, meat from FM (Exp. 1) had lower juiciness and FO (Exp. 2) had lower overall palatability. Protected sunflower meal protein with FO (Exp. 2) significantly lowered ratings for flavour, juiciness and overall palatability. Lamb meat with increased levels of long-chain omega-3 FA can be produced without altering the sensory quality (flavour or aroma) of the cooked meat.

Lipids and FA analysis of canine prostate tissue

It is widely reported that an association exists between dietary fat intake and the incidence of prostate cancer in humans. To study this association, there is a need for an animal model where prostate carcinogenesis occurs spontaneously. The canine prostate is considered a suitable experimental model for prostate cancer in humans since it is morphologically similar to the human prostate and both humans and dogs have a predisposition to benign and malignant prostate disease. In this study, the FA and lipids profiles of the normal canine prostate tissue from nine dogs were examined. The total lipid content of the canine prostate tissue was 1.7±0.5% (wet weight). The lipid composition analysis using TLC-FID showed that the two major lipid classes were phospholipids and TAG. Total FA, phospholipid, and TAG FA analysis showed that the major FA were palmitic acid (16∶0), stearic acid (18∶0), oleic acid (18∶1), linoleic acid (18∶2n−6), and arachidonic acid (20∶4n−6), The n−3 FA were present at <3% of total FA and included α-linolenic acid (18∶3n−3) (in total and TAG tissue FA), EPA (20∶5n−3) (not in TAG), and DHA (22∶6n−3) (not in TAG). The n−3/n−6 ratio was 1∶11, 1∶13, and 1∶8 in total, phospholipid, and TAG FA, respectively. This study shows the canine prostate has a low level of n−3 FA and a low n−3/n−6 ratio. This is perhaps due to low n−3 content of the diet of the dogs. FA analysis of dogfoods available in Australia showed that the n−3 content in both supermarket and premium bran dogfoods was <3% (wet weight), and the n−3/n−6 ratio was low.

Effects of dietary lipid type on muscle fatty acid composition, carcass leanness, and meat toughness in lambs.

Isonitrogenous amounts of two protein sources differing in rumen degradation rate and in lipid composition were fed to sheep with or without a rapidly fermentable cereal grain. The effects on intake, carcass leanness, and muscle fatty acid (FA) composition were examined. Thirty-eight crossbred wether lambs (9 mo, 35 to 48 kg) were allocated by stratified randomization to six treatment groups: 1) basal diet of alfalfa hay:oat hay (20:80) ad libitum = basal; 2) basal + lupin (358 g DM/d) = lupin; 3) basal + fish meal (168 g DM/d) = fish meal; 4) basal + barley (358 g DM/d) = barley; 5) basal + barley + lupin (179 + 179 g DM/d) = barley/lupin; or 6) basal + barley + fish meal (179 + 84 g DM/d) = barley/ fish meal. Lambs were fed individually. Dietary treatments were imposed for 8 wk, and the supplements were offered at 2-d intervals. Daily feed intake and weekly BW of lambs were recorded. At the end of the feeding period lambs were slaughtered after an overnight fast. Hot carcass weight (HCW) and fat depth (GR; total fat and muscle tissue depth at 12th rib, 110 mm from midline) were recorded. At 24 h postmortem samples of longissimus thoracis (LT) and longissimus lumborum (LL) muscles were taken from chilled (4 deg C) carcasses for the assessment of FA composition and meat tenderness, respectively. Lambs fed lupin or fish meal with or without barley had heavier slaughter weights (P < 0.004) and HCW (P < 0.001) than lambs fed basal or barley when initial BW was included as a covariate. The lupin diet also resulted in heavier carcasses (P < 0.05) than the fish meal or barley/fish meal diets. With GR as an indicator, fish meal and barley/ fish meal diets produced leaner carcasses (P < 0.01) than lupin and barley/lupin lambs. Long-chain n-3 FA content [20:5n-3 (P < 0.001), 22:5n-3 (P < 0.003), and 22:6n-3 (P < 0.001)] in the LT muscle were substantially higher with the fish meal and barley/fish meal diets, whereas muscle total n-6 FA was increased (P < 0.003) by lupin and barley/lupin compared with all other diets. Thus, increased muscle long-chain n-3 FA content occurred without an increase in fatness measured as GR, whereas increased muscle n-6 FA content was associated with an increase in carcass fatness. Under these circumstances, a reduction in carcass fatness had no effect on meat tenderness measured as Warner-Bratzler shear force.

Lipid, FA, and sterol composition of New Zealand green lipped mussel (Perna canaliculus) and Tasmanian blue mussel (Mytilus edulis)

The lipid, FA, and sterol composition of the New Zealand green lipped mussel (NZGLM, Perna canaliculus) and of the Tasmanian blue mussel (TBM, Mytilus edulis) were compared using TLC-FID and GC-MS. The respective mussel species were obtained from three different sites in both New Zealand (NZ) and Tasmania. Lipid class distribution of both mussel species was characterized by a high proportion of phospholipid (PL, 57–79%) and TG (10–25%), FFA (7–12%), and sterols (ST, 12–18%). The NZGLM had higher proportions of TG, FFA, and ST (P<0.01), whereas the TBM had a higher proportion of PL (P<0.01). There were higher proportions of total PUFA, saturated FA, n−3 FA, and hydroxy and nonmethyleneinterrupted FA (P<0.05) in the TBM compared with the NZGLM. The major FA in the NZGLM were 16∶0 (15–17%), 20∶5n-3 (14–20%), and 22∶6n-3 (11–17%). The same FA dominated lipids in the TBM, although there were significantly higher proportions of 16∶0 (P=0.000) and 22∶6 n−3 (P=0.003) and lower proportions of 20∶5n-3 (P=0.0072) in the TBM. A novel PUFA, 28∶8n-3, was detected in both mussels with higher amounts in the TBM, which probably reflects a greater dietary contribution of dinoflagellates for this species. Cholesterol was the dominant sterol in both mussels. Other major sterols included brassicasterol, 22-methylcholesterol, trans-22-dehydrocholesterol, and desmosterol. There were significant differences (P<0.05) between the NZGLM and TBM for 12 of the 20 sterols measured. Six sterols showed significant site differences for the NZGLM, and 10 for the TBM. The differences in the FA and sterol composition between the two species may be due to the diet of the NZGLM being more diatom-derived and the diet of the TBM having a greater dinoflagellate component.

Functional morphology of the gastric mills of carnivorous, omnivorous, and herbivorous land crabs

Terrestrial decapods consume a wide variety of plant and animal material. The potential adaptations of carnivorous, omnivorous, and herbivorous terrestrial crustaceans were studied by examining the functional morphology of the gastric mill. Two closely related species from each feeding preference group were examined to identify which features of the mill were due to phylogeny and which were due to adaptation. The morphology of the gastric mill matched the diet well; the gastric mills of the carnivorous species (Geograpsus grayi and Geograpsus crinipes) possessed a blunt, rounded medial tooth and flattened lateral teeth with a longitudinal grinding groove. These features make them well suited to a carnivorous diet of soft animal tissue as well as hard material, such as arthropod exoskeleton. In contrast, the mill of the herbivorous gecarcinids (Gecarcoidea natalis and Discoplax hirtipes) consisted of a medial tooth with sharp transverse ridges and lateral teeth with sharp interlocking cusps and ridges and no grinding surface. These features would efficiently shred fibrous plant material. The morphology of the mill of the omnivorous coenobitids (Coenobita perlatus and Birgus latro) was more generalized toward a mixed diet. However, the mill of B. latro was more adapted to deal with highly nutritious food items, such as nuts and heavily calcified decapods. Its mill possessed lateral teeth with extended ridges, which sat close to the calcified cardiopyloric valve to form a flattened floor. Hard items trapped in the mill would be crushed against this surface by the medial tooth.

The effect of vitamin : a deficiency on glucose uptake in the rat

This thesis describes an investigation of the effects of vitamin A deficiency on gut function, The central hypothesis to be tested was that acute vitamin A deficiency affects glucose uptake from the small intestine- The hypothesis was tested using a system involving perfusion of isolated segments of the small intestine in the anaesthetized rat. The system was used to study effects on glucose uptake under steady-state conditions. In the initial part of the study, experiments were diverted towards setting up the system for measuring steady-state uptake, and determining the relative contributions of active uptake and diffusion. Phenol red was found to be a reliable non-absorbable marker for determining net water movement. Phlorizin, generally at 1 mmol/L, was used as a competitive (reversible) inhibitor of active uptake. It is difficult however to confirm complete inhibition of active uptake by phlorizin because of the limited solubility of the inhibitor. The kinetics of glucose uptake f ram intra-luminal maltose were found to be, in general, not significantly different from those applying to the uptake of glucose from an equivalent glucose solution. Maltase activity in the perfused gut segment was found to be sufficient to hydrolyse most of the maltose (80 per cent or more) in the solution being perfused, a much greater proportion than was absorbed. Glucose absorptive capacity, measured on an intestinal dry weight basis, was greatest in the duodenum and progressively less in the jejunum and ileum. The rate of water uptake f ran the gut was increased by the presence of glucose in the lumen, and was linked to glucose uptake as shown by the inhibition of water uptake by phlorizin. Uptake of glucose by solvent drag was demonstrated by showing an increased rate of glucose uptake when the rate of water uptake was increased by perfusing a solution of reduced osmotic pressure. In the experiment a low intra-luminal glucose concentration was used to preclude net uptake by diffusion and active uptake was blocked with phlorizin. This process was further investigated using streptozotocin-diabetic rats in which the diabetes establishes a hyperosomotic blood with hyperglycaemia. Uptake by solvent drag was more obvious in diabetic animals. A back-diffusion (exsorption) of glucose from the tissues to the lumen was also shown; the rate being proportional to plasma glucose concentration. Vitamin A deficiency was established in weanling rats after 6-7 weeks feeding on a diet based on wheat starch, coconut oil, and casein washed with hot ethanol, together with vitamins and minerals. The vitamin A deficiency led to classic eye signs and was reversed by the addition to the diet of retinoic acid (5 g/g diet). Vitamin A deficiency decreased intestinal mucus production (dry weight) but had no detectable effect on the histology of the villous epithelium as shown under the light microscope. Using perfusion experiments it was shown that vitamin A deficiency had no significant effect on the rate of active uptake of glucose, but that deficiency increased the rate of passive uptake.

Nutrition, growth and production of Cherax Destructor Clark, 1936 (Decapoda, Parastacidae)

In this study the nutrition, growth and production of C. destructor was examined. Selected nutritional requirements of juvenile animals were determined under controlled conditions with the aim of developing a pelleted diet for use in hatcheries, nurseries and growout situations. The best developed diet was assessed for its potential as a supplementary feed for animals cultured in earthen environments. The protein requirements were first determined simultaneously with an evaluation of the effect of replacing animal protein (fishmeal) by soybean meal. Juveniles were reared communally for 59 d on isoenergetic diets containing 15-30% protein and graded levels of soybean meal (0-60%, of protein). When soybean meal was included at a level of 40-60%, growth was reduced relative to that achieved with control diets containing 15% and 20% protein, but this was not the case at a 20% soybean meal substitution level. A two-way interaction occurred between dietary protein and soybean meal content. Higher protein feeds enabled higher soybean meal inclusion levels without significantly affecting growth. Protein increases of 5% produced better growth at the 40% and 60% soybean meal substitution levels. This effect was less pronounced in the control and the 20% soybean meal diets. Carcass %protein increased and %lipid decreased as dietary protein increased. A similar effect occurred by increasing the soybean meal level to 60%. No obvious trend in carcass moisture, energy, and ash occurred. A protein requirement of 30% was apparent when fish meal and soybean meal were included in diets at levels of 20% and 24% (dry matter) respectively. Alternative protein sources to soybean meal were subsequently identified. Juveniles were maintained for 12 weeks on isoenergetic diets containing 30% protein and differing in the primary source of protein used, with meat, snail, soybean, yabby, and zooplankton meals comprising the major protein ingredient. No significant difference occurred in mean weight (MW), percentage weight gain (%WG), SGR or survival among diets. Food conversion ratios (FCR) were low, with a minimum value of 0.95 for the snail-based diet. The apparent net protein utilisation (ANPU) varied from 29.6% (zooplankton-based diet) to 41.2% (snail-based diet). Carcass composition varied with diet, with the greatest difference occurring in carapace colour. Animals fed the zooplankton-based diet developed the strongest, most natural pigmentation. A new combination of previously used protein-based ingredients was subsequently tested with reference to two yabby species, Cherax albidus and Cherax destructor, that were grown simultaneously in identical conditions. Juvenile male animals were reared individually for 20 weeks on isoenergetic diets containing 15% or 30% protein with fish meal, soybean meal, yabby meal and wheat products forming the basis of the diets. C albidus grew the fastest and utilised the food the most effectively. Carcass composition was influenced by diet with the 30% protein diet resulting in an increase in carcass protein and ash and a decrease in carcass lipid and energy relative to the low protein diet. Carcass moisture and calcium were not affected by diet. The intermoult period (IP) was highly dependent on the premoult weight (W) but the mean moult increment (WI, as weight) was independent of the PM. The orbital carapace length (OCL) and the abdominal length (ABL) %moult increments generally declined with an increase in PM whereas the propus length (PL) %moult increment generally increased. The IP, WI, %OCL, %ABL, and %PL moult increments varied according to diet and to species. Elevated dietary protein caused a reduction to the IP (for similar sized animals) by 11 d and 7 d and an increase to the WI by 85% and 81% in C. albidus and C destructor respectively. Dietary induced morphological changes also occurred. Animals of a standard OCL (both species) had significantly larger abdomens when fed the higher protein diet. Growth on the best developed diet was compared to the growth obtained on a natural diet of freshwater zooplankton. Juveniles were reared individually for 12 weeks on the two diets. The MW, %WG and SGR were higher for the zooplankton diet. Carcass composition was influenced by diet and the zooplankton fed animals had a higher carcass %protein, %lipid, %ash and %fibre content and were more richly pigmented than animals fed pellets. The IP and the WI were highly dependent on the PM and varied according to diet; feeding with zooplankton reduced the IP by 1.2 days and increased the WI by 13.7% compared to pellets. Nutrient digestibility was determined for the pelleted diets evaluated in the growth trials. Protein digestibility (PD) and dry matter digestibility (DMD), using chromic oxide (Cr2O3) as an exogenous marker, were high for all diets, at around 93% and 83% respectively. Ash digestibility varied considerably from 17% to 73% for the snail and yabby meal diets respectively. Crude fibre digestibility was around 50% and probably indicates cellulase activity. Alternative markers to Cr2O3 were evaluated. Ash was considered to be the most suitable alternative to Cr2O3, providing a reasonable, albeit lower, estimate of nutrient digestibility. Cr2O3 and ash were preferentially excreted whereas fibre was retained in the digestive system for a longer period, consequently, the collection of a particular fraction of the deposited faeces (late or early) substantially affected the digestibility coefficients. In earthen-based environments, animals fed the best developed diet were compared to animals cultured using a forage crop of clover (Trifolium repens). Three supplementary feeding strategies representing varying levels of management intensity were evaluated in a series of trials conducted in ponds and pond microcosms. Growth on pellets consistently exceeded that obtained with the forage crop, with final MW being 67-159% higher than that using clover and appeared to be the result of direct pellet consumption and from a pellet fertiliser effect (on the sediment). Within-pond DMD and PD were high and similar for each treatment (DMD = 51-58%; PD = 89-92%). In the control pond, DMD and PD increased with each successive flood. The faecal egestion rate (PER) decreased with each successive flood in all ponds, and is negatively related to animal weight and to foregut fullness (FF) according to power curves. FF was consistently lowest in the control pond. Mean FF was 48.5%, 62.3%, and 26.7% for the pellet, crop and control ponds respectively. FF increased to the third flood in each pond. The foregut protein content was high in all samples and the mean values were 33.9%, 32.7% and 35.6% for the pellet, crop and control ponds respectively. Foregut ash was highly variable within each pond and is inversely related to the foregut protein content. In the control and pellet ponds the highest foregut ash content occurred during flood 1. The culture system (aquaria or pond) strongly influenced the composition of the foregut content. The foregut of animals fed the manufactured diet (B2) in ponds contained approximately 176% more ash and 5% more protein than the foregut of animals fed in bare-bottom tanks. The FF of the tank fed animals was approximately 45% higher than the FF of pond fed animals after a similar feeding period. Base-line yields for extensive production systems appeared to be around 400kg ha-1. The supplementary addition of T. repens produced yields of approximately 635kg ha-1 (in ponds) to around 1086kg ha-1 (in tanks). The sequential addition of cut-clover to tanks stimulated growth to levels approaching those achieved on pellets. Yabbies stocked into ponds at 15-20 m-2 with a mean weight of 2.67g and fed a 30% protein pelleted diet for 100 d, resulted in a yield of approximately 1117kg ha-1, but only 2% of the population were above a marketable size of 50g. The feed utilisation indices were better for animals reared on pellets in bare-bottom tanks than in earthen environments, indicating some degree of pellet wastage when natural feeds are simultaneously present. High apparent food conversion ratios and low protein efficiency ratios occurred when the forage crop was provided. A considerable quantity of the dry matter and protein content of the forage crop was either inefficiently utilised or directed into other production pathways. Sowing a forage crop into pond microcosms to which a pelleted diet was also provided, did not enhance growth performance. Pelleted feed inputs at a rate of approximately 129g m-2 to 198g m-2 (dry matter) and 38g -2 to 64g m-2 (protein) over 70-100 d resulted in acceptable growth and feed utilisation indices for animals reared in ponds and pond microcosms. Forage crop inputs of approximately 533g m-2 to 680g m-2 (as dry matter) or 84g m-2 to 177g m-2 (as protein) over a 70-100 d period produced reasonable growth rates but poor feed utilisation indices. Low inputs of dry matter (from 113-296g m-2) and protein (from 24-54g m-2) from clover were sufficient to maintain high growth rates in pond microcosms for around 28 d. In ponds, a very low level of 21g m-2 (dry matter) and 4.3g m-2 (protein) was sufficient for around 3 weeks. Forage depletion appeared to occur beyond week 3-4 and was probably a major growth limiting factor. The mean hepatosomatic index (HSI) was 9.44, 7.68, and 6.79 for the pellet, crop, and control ponds respectively. The relationship between hepatopancreas weight and overall animal weight was significantly different between treatments. The hepatopancreas of pellet-fed animals had the highest %lipid and lowest %ash, %protein, %carbohydrate and %moisture content. In terms of absolute quantities, the only major difference in hepatopancreas composition between treatments occurred for lipid and dry matter content. The hepatopancreas of the pellet-fed animals was a cream/cream-yellow colour and was very fragile, whereas in the other ponds it was a more ‘natural’ bright yellow colour and was structurally more robust. C. destructor has a capacious foregut, being approximately 5 times the volume of similar sized Penaeids. The foregut volume (V, ml) of the yabby is related to animal weight (W, g) according to V = 0.048 W0.9543. Animals that were starved for 96 h and then fed diet B2 were almost completely foil after 30 min. The ‘apparent enzymatic response’ of animals fed various natural and artificial diets in tanks was evaluated. Nutrient processing time and the enzymatic response following ingestion appeared to be regulated by the chemical and physical properties of the diet. For the natural feeds, foregut protein was 1.2% higher (for zooplankton) and up to 300% higher (for detritus) than dietary protein, whereas ash was 7.5% higher (zooplankton) and 46-63% lower (detritus) than dietary ash. For animals fed diet B2 after 48 h without food, FF was approximately half that of 96 h starved animals after a similar feeding period but foregut protein and ash contents were similar. Finally, the physiological and morphological attributes elucidated in this study are discussed with reference to the ecology of the yabby. High growth rates, excellent feed utilisation indices and high digestibility coefficients for a wide range of diet-types illustrate nutritional flexibility. A capacious foregut, a large hepatopancreas with a high energy storage capacity, the ability to partition and preferentially excrete the low nutrient value inorganic component of the diet, the capacity to alter body form, nutrient processing time and enzymatic secretions in relation to diet-type, and modified behaviour according to feed availability also demonstrate plasticity/adaptability/flexibility. The combined effect of these important characteristics ensures survival in environments that may be adverse and highly variable in terms of nutrient availability. Collectively the morphological and digestive traits elucidated in this study reflect the generalist-type nature of C destructor and indicate that a polytrophic classification still seems appropriate. Several priority areas for further nutrition research are identified and recommendations are made regarding the best-practices to use in the commercial culture of the yabby. Of paramount importance is the further clarification of the nutritional requirements and feeding preferences of animals in various phases of development.

Control of ovarian development in the yabby (Cherax destructor)

A study under controlled conditions of ovarian development and rematuration in the yabby (Cherax destructot) was undertaken. The purpose of the study was to improve fundamental understanding of the reproductive biology of the species and provide a basis for application to hatchery management in culture. A review was made of the current status of yabby culture in Australia and the present understanding of reproductive biology of decapod Crustacea. The review emphasised factors controlling several aspects of ovarian development, in particular the processes of vitellogenesis. The subsequent study was designed within the context of current hatchery practice and was based on existing knowledge of decapod reproduction, The sexual differentiation of the yabby after hatching was investigated by serial histological sections, and experiments were carried out to investigate the possibility of sex reversal of males. Most of this Investigation was concerned with removing the influence of the androgenic gland in directing male development, with the intent of observing the development of the elementary gonadal tissue into ovary. It was found that in contrast to other crustacean species, the sex of the yabby becomes fixed before the development of external secondary sexual characteristics, and before the androgenic gland can be discerned. Ovarian tissue developed in females at less than 8 weeks after hatching. A preliminary examination was undertaken for feminising parasites in gonadal tissue of a hermaphrodite yabby. Investigation of the ovary after spawning demonstrated that whilst the female was held under constant conditions of temperature and photoperiod, little rematuration occurred. Except for generation of previtellogenic oocytes during the first two days, the gonaciosomatic index remained low for up to 5 months after spawning. If the temperature of the female was reduced to 10°C and maintained constant, the previtellogenic oocytes were partially resorbed over a three week period. Rematuration then commenced, albeit at a low rate because of the reduced temperature, A method for standardising gonadosomatic indices was developed which took into account differences in hepatopancreatic nutrient reserves of individuals and loss of one or more appendages. This part of the study also considered constraints to rematuration and developed a method of accounting for differences in the ability of females to remature after spawning. Experiments were carried out to investigate the effect of crowding and temperature manipulation on initiating ovarian rematuration and to determine the rate of rematuration at 22°C once initiated. The duration of low temperature had no effect on rematuration; an overnight cooling was sufficient to initiate the process, Rematuration to the end of stage 2 vltellogenesis was substantially complete within 10 days. Crowding of females suppressed rematuration, but less than ideal water quality was not found to have any effect. The presence of a male initiated rematuration at a similar rate, but also led to stage 3 vitetlogenesis and spawning. A study was made of the pheromonal influence of the male through water borne factors without success. Rematuration could not be induced in ovigerous females. The literature review indicated that ovarian rematuration was under the control of an ovary stimulating hormone produced by the thoracic nerve ganglia. Attempts were therefore made to stimulate ovarian rematuration by incorporating the thoracic nerve into the diet of females. Attempts were also made to induce the release of ovary stimulating hormone from the thoracic nerve with 5-hydroxytryptamine, and also with octopamine. No effects were found, but a significant difference between the neurophysiology of the yabby and northern hemisphere crayfish was observed, and the implications of this finding are discussed. The study did not produce any conclusive evidence of an ovary stimulating hormone for the yabby. A model of ovarian rematuration which collects the findings of the experimental investigations was developed, and was used to suggest a hatchery broodstock management protocol. This model differs from existing models in that rematuration triggers and nutritional status are considered.

Role of leptin receptors in the development of obesity

The focus of this dissertation was leptin and the leptin receptor, and the role of these genes (OB and OB-R) in the development of obesity and type 2 diabetes in humans and Psammomys obesus, a polygenic rodent model of obesity and type 2 diabetes. Studies in humans showed that circulating leptin concentrations were positively associated with adiposity, and independently associated with circulating insulin and triglyceride concentrations. Analysis of two leptin receptor sequence polymorphisms in a Caucasian Australian population and a population of Nauruan males, with very high prevalence rates of obesity, showed no associations between sequence variation within the OB-R gene and obesity- or diabetes-related phenotypic measures. In addition, these two OB-R polymorphisms were not associated with longitudinal changes in body mass or composition in either of the populations examined. A unique analysis of the effects of multiple gene defects in the Nauruan population, demonstrated that the presence of sequence alterations in both the OB and OB-R genes were associated with insulin resistance. Psammomys obesus is regarded as an excellent rodent model in which to study the development of obesity and type 2 diabetes in humans. Examination of circulating leptin concentrations in Psammomys revealed that, as in humans, leptin concentrations were associated with adiposity, and independently associated with circulating insulin concentrations. This animal model was utilised to examine expression of OB-R, and the regulation of expression of this gene after dietary manipulation. OB-R is known to have several isoforms, and in particular, OB-RA and OB-RB gene expression were examined. OB-RB is the main signalling isoform of the leptin receptors. It has a long intracellular domain and has previously been shown to play an important role in energy balance and body weight regulation in rodents and humans. OB-RA is a much shorter isoform of OB-R, and although it lacks the long intracellular domain necessary to activate the JAK/STAT pathway, OB-RA is also capable of signalling, although to a lesser degree than OB-RB. OB-RA is found to be expressed almost ubiquitously throughout the body, and this isoform may be involved in transport of leptin into the cell, although its role remains unclear. OB-RA and OB-RB were both found to be expressed in a large number of tissues in Psammomys obesus. Interestingly, obese Psammomys were found to have lower levels of expression of OB-RA and OB-RB in the hypothalamus, compared to lean animals. This finding raises the possibility that decreased leptin signalling in the brain of obese, hyperleptinemic Psammomys obesus may contribute to the leptin resistance previously described in this animal model. However, the primary defect is unclear, as alternatively, increased circulating leptin concentrations may lead to down-regulation of leptin receptors. The effect of fasting on leptin concentrations and gene expression of OB-RA and OB-RB was also examined. A 24-hour fast resulted in no change in body weight, but a reduction in circulating leptin concentrations, and an increase in hypothalamic OB-RB gene expression in lean Psammomys. In obese animals, fasting again did not alter body weight, but resulted in an increase in both circulating leptin concentrations and hypothalamic OB-RB gene expression. In the liver, fasting resulted in a large increase in OB-RA gene expression in both lean and obese animals. These results highlighted the fact that regulation of leptin receptor gene expression in polygenic models of obesity and type 2 diabetes is complex, and not solely under the control of circulating leptin concentrations. Sucrose-feeding is an established method of inducing obesity and type 2 diabetes in rodents, and this experimental paradigm was utilised to examine the effects of longer term perturbations of energy balance on the leptin signalling pathway in Psammomys obesus. Addition of a 5% sucrose solution to the diet of lean and obese Psammomys resulted in increased body weight in both groups of animals, however only obese Psammomys showed increased fat mass and the development of type 2 diabetes. The changes in body mass and composition with sucrose-feeding were accompanied by decreased circulating leptin concentrations in both groups of animals, as well as a range of changes in leptin receptor gene expression. Sucrose-feeding increased hypothalamic OB-RB gene expression in obese Psammomys only, while in the liver there was evidence of a reduction in OB-RA and OB-RB gene expression in both lean and obese animals. The direct effects of sucrose on the leptin signalling pathway are unclear, however it is possible to speculate that the effect of sucrose to decrease leptin concentrations may have been involved in the exacerbation of obesity and the development of type 2 diabetes in obese Psammomys, From these studies, it appears that sequence variation in the OB and OB-R genes is unlikely to be a major factor in the etiology of obesity in human populations. The ability to examine regulation of expression of these genes in Psammomys obesus, however, has demonstrated that the effects of nutritional modifications on leptin receptor gene expression need closer attention. The role of the OB and OB-R genes in metabolism and the development of type 2 diabetes also warrants further examination, with particular attention on the differential effects of dietary modifications on leptin receptor gene expression across a range of tissues.

Weaning and growth of Anguilla australis glass eels and elvers

Anguilla australis glass eels proved to be resilient and present strong aquaculture potential. General husbandry techniques, anaesthesia and prophylactic treatments were established for glass eels between 0.1 g and 2.0 g and elvers between 2.0 g and 8.0 g, caught in rivers and estuaries along the South East Coast of Victoria. The protozoan parasites Ichthyobodo and Trichodina were found to be present on arrival to the hatchery developed during different rearing treatments, and were successfully eradicated. A. australis glass eels accepted artificial food, but it was recommended first be fed a preweaning diet of minced fish flesh. A weaning regime from minced fish flesh to commercially available eel grower mash, over 15 days was established. Growth rate proved to be highly variable, both between and within groups. The highest growth rate of 2.71%/day was found when the natural diet of minced fish and Artemia was fed. The maximum growth rate when reared on an artificial diet of 1.63%/day was observed at 25°C. Growth was affected by the presence or absence of a preweaning diet, weaning diet, weaning period, temperature, but not by size or density. Once weaned, glass eels were found to perform better on commercially available grower mash than on the minced fish flesh, which was used to aid in weaning them to artificial diets. Of the water quality parameters measured stocking density was found to affect pH, Total Ammonia Nitrogen, Total Phosphorus, and Dissolved Oxygen, through not to an extent which affected growth.

Effects of dietary constituents on coronary heart disease risk factors

Coronary Heart Disease (CHD) is a major cause of death in Western countries. Mediterranean and Asian populations have a lower risk of death from CHD compared to Westernised population, as do vegetarian versus omnivorous populations. Dietary constituents of traditional diets consumed by these populations are thought to influence both the classical risk factors for CHD, and the more recently identified risk factors, such as oxidative modification of low density lipoprotein (LDL), LDL particle size, arterial compliance and haemostatic factors. The aim of this thesis was to examine the effects of several food components, particularly soybean and monounsaturated fat (MUFA), on CHD risk factors through 3 carefully controlled dietary interventions, and a cross-sectional study. A randomised crossover dietary intervention study was conducted in 42 healthy males to investigate the effect on CHD risk factors of replacing lean meat with tofu, a soybean product regularly consumed by Asian populations, while controlling all other dietary factors. The tofu diet resulted in significantly lower total cholesterol and triacylglycerol levels compared to the lean meat diet, and LDL particles that were more resistant to in vitro oxidative modification. However, insulin, fibrinogen, factor VII, and lipoprotein (a) were not significantly different on the 2 diets. A postprandial study was subsequently conducted to investigate any acute effects of a tofu test meal on the oxidative modification of LDL in 16 male subjects. There was no significant difference between the susceptibility of LDL to oxidative modification before and after the tofu meal. Twenty eight healthy subjects completed a separate randomised crossover dietary intervention comparing a high MUFA fat diet, using an Australian high oleic sunflower oil, with a low fat, high carbohydrate diet on CHD risk factors. The high MUFA oil diet significantly increased high density lipoprotein cholesterol compared to the low fat diet as well as producing LDL that were more resistant to oxidative modification. Neither the size of the LDL particle nor arterial compliance were significantly different on the 2 diets. Twelve matched pairs of vegetations and omnivores were also studies to compare the habitual diet of a low and higher risk population group, to compare their risk factors and identify dietary constituents that may explain the differences. The vegetarians consumed less saturated fat (SFA) and dietary cholesterol while consuming more polyunsaturated fat, dietary fibre and vitamin E compared to omnivores. The vegetarians had lower total cholesterol, LDL cholesterol and triacylglycerol levels compared to the omnivores and had LDL particles that were more resistant to in vitro oxidation. These findings contribute to our knowledge about the dietary constituents that can alter some CHD risk factors in healthy subjects, and which could reduce the risk of developing CHD. Investigations in high risk groups might reveal even more benefits.

Aspects of the life history of skates from southeastern Australia

The age and growth, reproduction and diet of several skate species in south-east Australia were studied. From studying these life history characteristics it was determined that skates have a relatively low productivity and may therefore be at risk of local extinction if increasingly exploited without appropriate management.

Effects of a fox removal program on small and medium-sized mammal population dynamics within the Anglesea Heathlands, Victoria

This thesis assessed the diet of foxes within the ALCOA lease area of Anglesea to determine which native and introduced species foxes were eating. Results showed that Swamp Wallaby was regularly eaten but many other mammals, birds, insects and reptiles were also consumed. The response of native mammals to seasonal fox removal was also determined.

Aspects of the ecology of the Wedge-tailed Eagle, Aquila audax, in southern Victoria

This study investigated the nest site selection characteristics and diet of the Wedge-tailed Eagle, Aquila audax, in southern Victoria. It was found that sites where local topography afforded some protection from adverse weather and where the nest tree was live were most commonly selected. Rabbits were found to the major prey item of this eagle.